Abstract

Low-temperature thermoelectric properties are reported for polycrystalline samples of chalcogenide spinel (X = S, Se; = 8.0 to 4.0). For all samples with X = S, the electrical resistivity behaves similarly to that of a doped semiconductor at high temperatures and shows a variable-range-hopping-type (VRH) temperature dependence at low temperatures. The values of and the thermopower decrease concomitantly with decreasing initial Cu composition . For of the sample with X = Se, shows VRH behavior in a wide temperature range. Because of the monotonic increase of as and the exponential decrease of with increasing temperature due to the the VRH conduction, the sample with X = Se can be a good high-temperature thermoelectric material. Furthermore, both systems show a low thermal conductivity of 1.5 W/Km because of their complex structures.